These can be used to create 'long exposure' shots where it takes a full (short) video and merges it all into a single picture. Here's my first attempt to take a picture of star trails by looking at a planet's north celestial pole - I didn't have a long enough video to cover a full revolution in this case, but it did at least prove the concept worked.

Here's a more complete shot from another planet. No horizon here as I was looking straight up into the sky, but it's a few full revolutions. The blue/brown hazy outer region is the smeared out band of the galactic disk and bulge rotating in the sky along with the stars.